Bristol, beautiful Bristol, hasn't had the art shows it deserves. I can't put that observation more politely. For years, while other major cities were going forward (more or less), Bristol's subsidised galleries were apparently still stuck in a throwback art of texts and interventions, mimsy media critiques and bits of fluff on the gallery floor: in short, with the most anorexic of conceptualism.

There were exceptions. The Arnolfini showed Rachel Whiteread, Louise Bourgeois and others in the misty past. But it feels an age since it offered vivid enticements. Could Bristol's one big venue for contemporary art really believe that what the city needed in 2002 was a comeback show for Victor Burgin, that most relentless and prolix of Seventies theorists? Surely this was the glummest of all low-points.

And so it now seems. For the Bristol art scene, growing even before then, has never looked stronger. There are many small galleries, sprinters compared with the necessarily slow-paced Arnolfini; and the artists' colony of Spike Island now has a showplace in the A Bond warehouse. Richard Long, Martin Parr and Mariele Neudecker are all based here. Earlier this year, Beck's Futures had one of its three simultaneous exhibitions in Bristol. And the British Art Show, now in its sixth incarnation, has taken up residence all over the city.

The most compelling art in Bristol now, though, is by German-born Mariele Neudecker. Known for her great visions miniaturised in liquid-filled tanks - snow-capped mountains, plunging gorges, motes twinkling deep within forest glades - Neudecker has made a tremendous career out of these submerged theatres of the unconscious.

Her latest works at Colston Hall are based upon, and accompanied by, Mahler's Songs on the Death of Children, each of which has some connection with light. In one installation, a tiny, flickering image is projected on a doorknob - the height and light of the departed child - while in another film-loop, framed in shivering curtains, darkness becomes visible over mountain tops in a never-ending presentiment of grief. 'Look at us well, for soon we will be far away.' As Kathleen Ferrier sings of lost children's bright remembered eyes, a vision of treetops swaying against the evening sky plays across a brilliant oval mirror. Lightning flashes intermittently, dazzling, ephemeral, and a bird flies up and out of sight. Where do we go from here if not the sky, the heavens? The child's innocent belief is the adult's mortal question, given visual expression in this eye-shaped view of oblivion.

These works could so easily have descended into illustration, but they succeed even without the Mahler. A film of alpine flowers against clear skies is almost entirely obscured by a high wooden fence, allowing only tantalising glimpses. The scene dissolves, the screen fades to a kind of twilight - still glowing, but entirely blank; as precise a representation of being untimely ripped from a beautiful dream to dawning sorrow as can be imagined.

It is hard to think of another contemporary artist able to give form - and, I think, consolation - to such agonising grief. Neudecker shows herself as remarkably gifted with film as with model-making and sculpture. I don't know why she never wins the Turner Prize, still less why she doesn't make it to the shortlist.

On the other hand, you need only consult the British Art Show to see the rubber-stamped art of the day: what the Tate shows, what regional curators endorse, what the Arts Council purchases. Indeed, since this show started last year, three of its artists have cropped up on the Turner shortlist - Mark Titchner, who had a recent show at the Arnolfini; Tomma Abts whose trompe l'oeil abstracts (a neat paradox) are beginning to get under my skin; and Phil Collins, whose video of a dance marathon in Ramallah (the contestants get tired, but the misery goes on: a simplistic metaphor) is so ubiquitous it might as well be on national cinema release.

The sixth of these five-yearly shows is more political, and international, than any other. Its best works are mainly videos - Uganda, domestic life in Nazareth, money in Istanbul - that could almost be travelogues. The rest is what it always is: depressingly variable. And so various you couldn't possibly make any deductions about the current state of British art (the besetting temptation of such surveys) except that many of these artists don't necessarily want you to think they're any good.

Which heaven forfend. But Bristol has chosen from among the best to make new works especially for the city. At Station, a tiny boathouse turned gallery, Scottish sculptor Claire Barclay has crammed a flotsam-and-jetsam assemblage in between doorway and fireplace like some gigantic version of a bottled ship. A wrecked thing, all skewed spars and torn sails, it encapsulates the city's merchant history - the sails are rawhide, the anchor a manacle, the domes and spires of the city laid out in brass weights. Yet despite the heavy hints of slavery, it still manages to come across as abstract.

Hew Locke's gambit, which is to trick out famous icons with bright plastic gewgaws until they completely lose face, has never been put to better use than in Bristol. Locke has made over photos of the city's statues with glitzy tat. Edmund Burke, former local MP, is decked in bling, his complex views on democracy awarded a semi-sardonic cake decoration: Congratulations! Slave-owner Edward Colston, of Colston Hall, is barely visible beneath an imprisoning mass of costume jewellery - turned to gold like Midas.

The vitality of the Bristol scene is partly to do with these shrewd local commissions. Plan 9 have devised Wig Wam Bam!, a show specifically for the city's eerie Elizabethan manor, Red Lodge. Naturally, the place has to have ghosts and there are some helplessly unfrightening figures of children. But the strongest works are the simplest. Nicola Donovan's elaborate bonnets turn out to be twisted from real tresses, as if hair - so bodily, yet so alien - had a life of its own. Richard Box strings a cordon of bood-red neon across stately-home chairs. It fulfils the usual keep-off function to an unusual degree, with its overtones of electric fencing. But it also vibrates, fairly crackles, with a livewire presence: midway between joke and visual epigram.